It is known that the presence of a significant amount of organic material in Bayer process liquor causes numerous problems. These problems include lower productivity of alumina; generation of an excessive proportion of fine alumina particles; higher impurities contents in the liquor and alumina; lower red mud settling rate; loss of caustic due to the formation of sodium organic compounds; increased liquor density, viscosity and boiling point and foaming of the liquor.
Numerous methods have been developed in the prior art for controlling organic compounds in Bayer process liquor. However, each of these prior art methods suffers from one or more serious limitations making it less than entirely suitable for its intended purpose.
For example, Inao et al U.S. Pat. No. 4,215,094 discloses a method for removing organic substances from an alkali aluminate solution wherein the solution is oxidized in the presence of a catalyst comprising copper ions. However, recovery of the copper ions from the solution requires addition of a chemical substance which reacts with the copper ions to form a water-insoluble precipitate. This chemical substance is generally a sulfide, which is itself an undesirable contaminant.
Some other methods for controlling organic compounds in Bayer liquor disclosed in the prior art are bauxite roasting (Hall U.S. Pat. No. 663,167); adsorption of liquor impurities onto activated alumina (Emerson U.S. Pat. No. 3,832,442); and addition of a soluble barium salt to the liquor (Mercier et al U.S. Pat. No. 4,101,629).
It is a principal objective of the present invention to provide a process for enhancing the wet oxidation of organic contaminants contained in a sodium aluminate solution.
An advantage of the invention is that the process does not require addition of copper ions, sulfides or other contaminants to the solution.
Additional objects and advantages of the present invention will become apparent to persons skilled in the art from the following specification and claims.